Positively thinking, she may have been passing a tough days for her Mom who is not getting well. Please discuss with her if she has any genuine problem from home front. If so, please tell her that the project she is looking after has some target date to complete. If she is unable to do so, the same can be taken away from her to get done by someone. Give her a certain time to get disciplined. If her attitude is for other non-understandable reasons, you can talk to your higher-ups for disciplinary actions.
Asim